1. Field of the Invention
This invention relates to a key code generator for electronic musical instruments.
2. Description of the Prior Art
Conventional key code generators have usually employed, as a method for detecting closed key switches, the key code multiplex method that information of the closed state of the key switches is rendered by time-division scanning of the respective key switches into a TDM (Time-Division Modulation) signal or a PCM (Pulse Code Modulation) signal synchronized therewith. With the key code multiplex method, however, one scanning period is needed for obtaining information necessary for time-division scanning of the respective key switches for detecting the open and closed states of the key switches. In the case of an ordinary electronic organ, if the key switches are divided into blocks and if the player uses each of his arms for two blocks and his feet for one block, five blocks are needed at most. For example, if the key switches are divided into groups every octave, they are divided into seventeen blocks including 61 upper keys, 61 lower keys and 25 foot keys. It is apparent that at least twelve blocks do not take part in playing. Therefore, it is sufficient to scan only five blocks. Further, sending of time-division clock pulses to the key switches is subject to a restriction by the characteristics of the switches, that is, their chattering and time constants, with the result that an erroneous operation is liable to occur due to a waveform distortion and that the limit of high-speed operation by the circuit integration is suppressed low. Moreover, in the case of flowing a high-frequency clock pulse between the switch and the circuit, it may become a noise source with respect to other circuits.